(a) To set up a coffee cup calorimeter experiment, we like a substantial tempera

Question

(a) To set up a coffee cup calorimeter experiment, we like a substantial temperature change so that the measurement is accurate, but not too large to avoid the water boiling. In this problem we calculate the final temperature change. When solid sodium hydroxide dissolves in water, the H for the solution process is -44.4 kJ/mol of NaOH. If a 13.9 g sample of NaOH dissolves in 250.0 g of water in a coffee-cup calorimeter initially at 23.0C. What is the final temperature of the solution? Assume that the solution has the same specific heat as liquid water (4.184 J/(g·K))

(b) Dissolution is endothermic for many salts (e.g., ammonium nitrate from lecture). Why do you think dissolution of NaOH is exothermic? Your answer should be in terms of the strengths of intermolecular interactions that are broken and formed when these salts dissolve.

Explanation / Answer

moles of NaOH = 13.9 / 40 = 0.348

delta H = - Q / n

-44.4 =- Q / 0.348

Q   = 15.4 kJ

Q = m Cp dT

15429 = 250 x 4.184 (T2 - 23.0)

T2 = 37.8 oC

final temperature = 37.8 oC

b)

NaOH is strong electrolyte it is readily soluble in water forms Na+ and OH-

in intermolcular forces of ions -dipoles Na+ and partially negative charged O and OH- and partially positive charged ions are greater . so it is more exothermic reaction

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